Linear motion bearing segment

ABSTRACT

A linear motion bearing assembly ( 20 ) as provided for movement along a splined shaft ( 10 ). The rolling element retainer of the bearing assembly ( 20 ) is assembled from a plurality of arcuate interengageable self-contained rolling element retainer segments ( 22 ). Each of the rolling element retainer segments ( 22 ) includes at least one rolling element track ( 30 ) having a load bearing portion ( 34 ) and a return portion ( 36 ). At least one load bearing plate ( 44 ) is axially positioned in each segment and serves to receive and transmit loads from the bearing rolling elements ( 32 ) in the load bearing portion ( 34 ) of the ball tracks ( 30 ). An extended housing retainer structure encloses all of the exposed exterior surfaces of the rolling element retainer segments ( 22 ) and is configured and dimensioned to maintain the rolling element retainer segments ( 22 ) in position and to receive a load either directly or indirectly from the load bearing plates ( 44 ).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional applicationSer. No. 60/242,850 filed on Oct. 24, 2000, the entire contents of whichare hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to linear motion bearing and, moreparticularly, to linear motion bearing assemblies made up of bearingsegments for longitudinal movement along a splined shaft.

2. Background of Related Art

The present invention is directed to an improved linear motion bearingsassembly for use on a splined shaft. In particular, the improvementsrelate to biased linear motion bearing assemblies of the type whichsupport a carriage or a pillow block for linear movement along anelongated splined shaft. These bearing assemblies can either be of theopen type or the closed type.

Typical linear rolling bearing assemblies include a series of rollingelements moving about a circulation path which circulation path isformed in the periphery of a track member and a surrounding andenclosing bearing cover confining the rolling elements in theirrecirculation path. In order to achieve an accurate linear motion, theaxis of the bearing assembly must be precisely aligned with the desireddirection of motion along the supported structure. In addition thisprecise alignment also minimizes skewing forces acting on the bearingassembly, which skewing forces tend to reduce the load/life performanceof the bearing assembly.

Installation of such bearing assemblies on a supporting structure (i.e.,shaft, splined shaft, guideway or rail) typically involves precisionmachining of locating surfaces in order to properly align the bearingassembly on the supporting structure. Such bearing assemblies aretypically installed in sets, each comprised of a number of variouslyfacing bearings such as to engage a series of surfaces on the supportingstructure (i.e., such as above and below a supporting surface and/oralong a lateral edge of a supporting surface). In such instances it isusual to provide a bearing adjustment for enabling precision adjustmentof the bearing assembly on the supported structure and also forestablishing a proper bearing pre-load by adjusting an opposing bearingassembly for reasons well known to those skilled in the art. In suchinstallations, considerable precision machining of the supportedstructure is necessitated which is difficult and expensive to accomplishon the supporting structures.

Additional prior art bearing assemblies typically include an outerhousing and at least one ball retainer dimensioned for insertion intothe outer housing. The rolling element retainer has at least one balltrack in a loop configuration for containing and recirculating bearingballs therein. The ball tracks typically include open portions whichfacilitate a load transfer from a supporting shaft to a load bearingstructure such as load bearing plates operatively associated with eitherthe ball retainer or the outer housing while return portions of the balltracks permit continuous recirculation of the bearing balls through theball tracks during linear motion.

In some embodiments, the ball retainer is formed as a monolithic elementwith the ball tracks integrally incorporated therein. See, U.S. Pat. No.3,767,276 to Henn. This structure, however, is difficult to efficientlymanufacture because of the complex molds required. Also, these ballretainers, prior to insertion into a mounting carriage or outer housingare necessarily open and thus exposed to ambient conditions andcontaminants such as dust and dirt. Such exposure could deleteriouslyaffect the operation and life of the bearing assembly as well as thesupport structure on which it moves.

Self-contained linear bearing units are also known in the art. See, e.g.U.S. Pat. No. 4,815,862 to Mugglestone et al. This unit, whilerepresenting a marked improvement in the art, still requires the use ofend caps to engage the load bearing plates of the bearing segments.Further, the load bearing plates must be precisely machined to properlyinter-fit with the end caps. This configuration adds to the expense andcomplexity of the bearing.

The load bearing structure may be in the form of integral elementsformed on an inner radial surface of the outer housing. Typical bearingassemblies utilizing load bearing structures formed in the outer housingare shown, for example, in commonly owned U.S. Pat. No. 5,046,862 to Ng,the disclosure of which is incorporated herein by reference.

In lieu of integral load bearing structure, separate load bearing platesmay be used to transfer loads from the supporting shaft. These loadbearing plates are longitudinally oriented in association with the ballretainer so as to engage at least those bearing balls in direct contactwith the support shaft. These load bearing plates may also be configuredto be axially self-aligning by providing structure which permits theplates to rock into and out of parallelism with the longitudinal axis ofthe ball retainer. See, for example, commonly owned U.S. Pat. No.3,545,826 to Magee et al. Individual load bearing plates may be expandedtransversely so as to engage bearing balls in corresponding adjacentload bearing tracks. In this form, parallel grooves are formed in theunderside of the plates to guide the bearing balls while they are in theload bearing portion of the ball tracks. See, for example, U.S. Pat. No.3,951,472 to Schurger et al.

Accordingly, it is an object of the present invention to provide alinear motion bearing segment which can be easily and efficientlymanufactured.

It is another object of the present invention to provide a linear motionbearing assembly having a rolling element retainer and outer housingwhich are easily fabricated using engineering polymers, powder metal orinsert molding.

It is a further object of the present invention to provide a low costlinear motion bearing assembly having a high load bearing capacity andhaving self-aligning capability.

It is yet another object of the present invention to provide a bearingassembly which eliminates the need for extremely high precision rollingelement/guideway (rail) bearing assemblies and their resultant expensivemanufacturing costs.

These and other highly desirable objects are accomplished by the presentinvention in a linear motion bearing assembly having a plurality ofrolling element tracks and individual bearing plates arranged in arolling element retainer and enclosed by a low cost outer housing whichserves to protect the rolling elements, rolling element tracks and loadbearing plates without having to transmit loads from the bearing rollingelements to the carriage block into which the bearing assembly ismounted.

Objects and advantages of the invention are set forth in part herein andin part will be obvious therefrom, or may be learned by practice withthe invention, which is realized and attained by means ofinstrumentalities and combinations pointed out in the appended claims.The invention comprises the novel parts, constructions, arrangements,combinations, steps, processes and improvements herein shown anddescribed.

SUMMARY OF THE INVENTION

The present invention provides for a linear motion bearing segmentconfigured and adapted for movement along a splined shaft, guideway orrail. A rolling element retainer structure of the bearing assembly canbe either monolithically formed or, alternatively, assembled frommultiple elements. In a first multi-element embodiment, the rollingelement retainer structure is made up of a pair of quarter arcuaterolling element retainer segments and a half arcuate rolling elementretainer segment. In an alternate multi-element embodiment, the rollingelement retainer structure is made up of a pair of half arcuate rollingelement retainer segments. At least a portion of the axial rollingelement bearing tracks are formed in the rolling element retainerstructure and, preferably, the complete rolling element bearing tracksare formed therein.

The linear motion bearing assembly further includes an outer housingsleeve which substantially encloses all of the rolling element retainerstructure. The housing sleeve is preferably formed of an engineeringpolymer and serves to protect the rolling element retainer and bearingrolling elements contained therein from ambient contamination.

A plurality of load bearing plates are axially positioned within theouter housing and serve to receive and transmit loads from the bearingrolling elements to the load bearing portion of the rolling elementbearing tracks. Each load bearing plate is at least partially retainedin the linear motion bearing assembly by retaining features which aredisposed at least partially around the rolling element retainerstructures and which retain at least a portion of the load bearingplates. Preferably, the load bearing plates and/or plate retainingfeatures are configured and dimensioned such that the linear motionbearing assembly is substantially self-aligning on the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, referred to herein and constituting a parthereof, illustrate the preferred embodiments of the linear motionbearing segment of the present invention and, together with thedescription, serve to explain the principles of the invention.

FIG. 1 is an exploded perspective view of a linear motion bearingsegment, with the housing removed, in accordance with one embodiment ofthe present invention;

FIG. 2 is a transverse cross-sectional view of an assembled linearmotion bearing segment shown in FIG. 1;

FIG. 3 is an exploded perspective view of a half bearing segment of thelinear motion bearing segment shown in FIG. 1;

FIG. 4 is a perspective view of the linear motion bearing segment withthe housing removed and in place in a splined shaft;

FIG. 5 is an end elevational view of the linear motion bearing segmentshowing the internal elements of the bearing segment in phantom;

FIG. 6 is a transverse cross-sectional view of a linear motion bearingsegment in accordance with a second embodiment of the present invention;and

FIG. 7 is an exploded perspective view of the half bearing segment ofthe linear motion bearing segment shown in FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals identifysimilar structural elements of the subject invention, there isillustrated in FIGS. 1-5 a closed-type linear motion bearing segmentconstructed in accordance with a preferred embodiment of the presentinvention and designated generally by the reference numeral 20. As usedherein, the term ball and rolling element are intended to be usedinterchangeably and encompass namely, ball bearings, roller bearings,needle bearings, axle bearings, etc. While a closed-type linear motionbearing segment is disclosed, it is envisioned that an open type linearmotion bearing segment can be constructed in accordance with the presentdisclosure.

Linear motion bearing segment 20 is fabricated from a pair of individualquarter arcuate interengageable self-contained ball retainer segments 22and a half arcuate interengageable self-contained ball retainer segment24 all of which are supported in interengageable association within ahousing 26. The housing 26 includes a longitudinal groove 18 formedalong an inner surface thereof for engaging the half arcuate retainersegment 24. Stated differently, the linear motion bearing segment 20 isfabricated from a pair of 90° arcuate interengageable self-containedball retainer segments 22 and a single 180° arcuate interengageableself-contained ball retainer segment 24. When fully assembled, thequarter segments 22 and the half segment 24 for a linear motion bearingsegment 20 are adapted and configured to move on a splined shaft 10without rotational motion of the bearing segment 20 relative to alongitudinal axis of the splined shaft 10. Further, although shown as aclosed-type bearing, an open-type bearing could be readily fabricatedusing such self-contained segments.

Each quarter segment 22 includes an inner portion 28 having an innersurface configured and adapted to be in clearance to the adjacentquarter arcuate portion of the outer surface of the splined shaft 10,the inner portion 28 defining a ball bearing track 30 formed therein andwhich ball bearing track 30 retains a plurality of bearing balls 32. Theball bearing track 30 is made up of a load bearing portion 34 and areturn portion 36 interconnected by turnarounds 38. An outer lid portion40 is adapted and configured to engage the inner portion 28 and includesa load bearing plate mounting aperture 42. By way of example only, theouter lid portion 40 can be snap fit into engagement with the innerportion 28. However, other engagement mechanisms, such as pins, grooves,adhesives, etc. are also contemplated and are within the scope ofknowledge of one skilled in this art.

A load bearing plate 44 is dimensioned and configured to fit intoaperture 42 of outer lid portion 40 of each quarter bearing 22. A pairof longitudinal grooves 46 are formed in the side walls of each loadbearing plate 44, which grooves 46 receive projections 48 formed in theperiphery of aperture 42. Each load bearing plate 44 preferably includesat least one longitudinal track 50 formed in an inner surface thereof.This longitudinal track 50 serves as the upper surface of the loadbearing portion 34 of the ball track 30. The plurality of bearing balls32 are positioned in ball track 30 and, when in the load bearing portion34, serve to transmit loads from the load bearing plates 44 to thesplined shaft 10 as well as to facilitate reciprocal longitudinal motiontherealong.

As seen in FIGS. 1 and 2, and in particular in FIG. 3, the half arcuateball retainer segment 24 includes a base portion 52 having an innersurface configured and adapted to be in substantial clearance of spline12 formed along a longitudinal length of the shaft 10. The base portion52 includes an outer surface defining a pair of independent ball bearingtracks 54 formed therein and which ball bearing tracks 54 retain aplurality of bearing balls 56. Each ball bearing track 54 is made up ofa load bearing portion 58 and a return portion 60 interconnected byturnarounds 62. The respective load bearing portions 58 are locatedadjacent to one another and are spaced from one another by a retainingmember 64 formed longitudinally along the base portion 52.

The half arcuate ball retainer segment 24 further includes a single loadbearing plate 66 having an inner surface configured and adapted to bedisposed over both load bearing portions 58 of each ball bearing track54 and an outer surface defining a pair of longitudinally extendingconvergent flat portions 68 and 70. Each convergent flat portion 68 and70 is configured and adapted to engage a biasing spring 72. In addition,the half arcuate ball retainer segment 24 further includes a pair oflids 74 and 78, which lids 74 and 78 serve to close the half retainersegment 24. Each lid 74 and 78 includes a window 80 for receiving one ofthe convergent flats 68 and 70 respectively of the of the load bearingplate 66 and through which window 80 each biasing spring 72 can extendto contact the inner surface of the housing 26. (See FIG. 4)

In use, each biasing spring 72 applies a pre-load to the bearing balls56 through each convergent flat 68 and 70 of the load bearing plate 66.The pre-load being applied against opposite sides 14 and 16 of thespline 12 at an angle “θ” in a range of between about 25° to about 75°.(See FIG. 2). While the biasing spring 72 is shown as a corrugated leafspring, it is envisioned that other biasing springs may be substitutedincluding resilient plastic filler, coil springs, torsion springs, etc.,with corresponding adaptations to the housing and bearing plates.

Although shown herein in a half bearing segment configuration, it isalso contemplated that other sizes can be used including quarters orthirds and that the segments can be arranged to accommodate multiplesplines on an elongate shaft.

Referring now to FIGS. 6 and 7, there is illustrated a closed-typelinear motion bearing segment constructed in accordance with a furtherembodiment of the present invention and designated generally by thereference numeral 100. The linear motion bearing segment 100 isfabricated from a pair of individual half arcuate interchangeableself-contained ball retainer segments 102 supported in interengageableassociation within a housing 104. When fully assembled, the halfsegments 102 are adapted and configured to move on a splined shaft 106,having a substantially “I” shaped cross-section, without rotationalmotion of the bearing segment 100 relative to a longitudinal axis of thesplined shaft 106. Further, although shown as a closed-type linearbearing, an open-type linear bearing could be readily fabricated usingsuch self-contained segments.

Each half segment 102 includes an inner portion 108 having an innersurface configured and adapted to be in substantial clearance of alateral half of the splined shaft 106 and an outer surface defining apair of independent ball bearing tracks 110 formed therein. Each ballbearing track 110 is made up of a load bearing portion 112 and a returnportion 114 interconnected by turnarounds 116. The respective loadbearing portions 112 of each inner portion 108 are located adjacent toone another and are spaced from one another by a dividing member 118.

Each half segment 102 includes an outer lid portion 120 configured toengage inner portion 108 and includes a load bearing plate aperture 122.In the embodiment depicted in FIGS. 6 and 7, engagement of each outerlid portion 120 to each inner portion 108 is accomplished by throughholes 124 formed in the outer lid portion 120 and pegs 126 extendingfrom an outer surface of the inner portion 108 configured and adapted toengage the through holes 124. Other engagement mechanisms, such as pins,grooves, adhesives, etc. are also contemplated and are within the scopeof knowledge of one skilled in the art.

Each half segment 102 includes a load bearing plate 128 dimensioned andconfigured to fit into the load bearing plate aperture 122 of outer lidportion 120 and adapted to be disposed over both load bearing portions112 of each ball bearing track 110. The load bearing plate having acentral body portion 132 and a pair of longitudinally extendingdivergent flat portions 134. An inner surface 130 of the load bearingplate preferably includes a pair of longitudinal tracks 136 which serveas an upper surface of the load bearing portion 112 of the ball track110.

Meanwhile, the outer surface 132 of the load bearing plate 128 isconfigured and adapted to engage a biasing spring 138. The biasingspring 138 includes a elongate body portion 140 and a pair of elongatediverging corrugated leaf portions 142. The diverging leafs 142 of thebiasing spring 138 are configured and oriented such that each leafportion 142 engages a respective divergent flat portion 134 of the loadbearing plate 128. A plurality of bearing balls 144 are positioned ineach ball bearing track 110 and, when in the load bearing portion 112,serve to transmit loads from the load bearing plates to the splinedshaft 106 as well as to facilitate reciprocal longitudinal motiontherealong. The housing 104 includes a pair of opposed “V” shapedprotrusions 146 extending inwardly from an inner surface thereof andconfigured and adapted to engage an outer surface of the elongate bodyportion 140 of each biasing spring 138. The “V” shaped protrusionpresses the biasing spring 138 such that the diverging leaf portions 142press against the divergent flat portion 134 of the outer surface ofload bearing plate 128.

In use, each biasing spring 138 applies a pre-load to the bearing balls144 through each diverging flat portion 134 of the load bearing plate128. The pre-load being applied at each juncture 148 of the “I” shapedshaft 106 between the pair of horizontal portions 150 and theinterconnecting web portion 152 at an angle “φ” in a range between about25° to about 75° and more preferably about 45°. (See FIG. 6). Onceagain, while the biasing spring 138 is shown as having a pair ofcorrugated leaf springs, it is envisioned that other biasing springs maybe substituted including resilient plastic filler, coil springs, torsionsprings, etc.

It is envisioned that both the base portion 52 and the lids 74 and 78 ofthe half bearing segment 24 of the first embodiment and the innerportion 108 and outer lid portion 120 of the second embodiment arepreferably formed from an engineering polymer to facilitate ease ofmanufacture.

To the extent not already indicated, it also will be understood by thoseof ordinary skill in the art that any one of the various specificembodiments herein described and illustrated may be further modified toincorporate features shown in the other specific embodiments.

The invention in its broader aspects therefore is not limited to thespecific embodiments herein described but departures may be madetherefrom within the scope of the accompanying claims withoutsacrificing its chief advantages.

1. A linear motion bearing assembly for movement along a guide way, arail or a splined shaft, comprising: a ball retainer structure formed ofa plurality of self-contained ball retainer segments, each of said ballretainer segments including an inner portion defining at least one balltrack having an open load bearing portion, an open return portion, andturnarounds interconnecting said load bearing and return portions, andan outer lid portion defining a load bearing plate aperture formedtherein; a load bearing plate positioned at least partially in said loadbearing plate aperture of each outer lid portion such that said loadbearing plate is positioned adjacent said load bearing portion of saidball track; a plurality of bearing balls disposed in said ball tracksfor transmitting a load from said shaft to said load bearing plate andfor facilitating a movement of said linear motion bearing assembly alongsaid rail; an extended housing retainer structure enclosingsubstantially all of an exposed exterior surface of said ball retainerstructure and having an inner surface in direct contact with said outerlid portions, said extended housing retainer structure being configuredand dimensioned to maintain said outer lid portions in position and forreceiving said load either directly or indirectly from said load bearingplates; and biasing means disposed between said bearing plate and saidinner surface of said extended housing retainer structure, wherein saidbiasing means extends through said aperture in at least one of saidouter lid portions, and wherein each biasing means applies a pre-load tothe plurality of bearing balls disposed in said ball tracks.
 2. Thelinear motion bearing assembly of claim 1, wherein said ball retainerstructure is formed of a pair of individual quarter arcuateinterengageable self contained ball retainer segments and a half arcuateinterengageable self contained ball retainer segments.
 3. The linearmotion bearing assembly of claim 2, wherein said half arcuate retainersegment includes a pair of ball tracks and one load bearing plate. 4.The linear motion bearing assembly of claim 3, wherein said load bearingportion of each of said pair of ball tracks in said half arcuateretainer segment are arranged in side-by-side configuration within saidhalf arcuate retainer segment and are separated from one another by adividing member formed in said inner portion of said half arcuateretainer segment.
 5. The linear motion bearing assembly of claim 4,wherein said inner portion of said half arcuate retainer segment isconfigured and adapted to mate with a spline formed along a length ofsaid shaft.
 6. The linear motion bearing assembly of claim 4, whereinone of said load bearing plates simultaneously engages said load bearingportion of each of said pair of ball tracks.
 7. The linear motionbearing assembly of claim 6, wherein load bearing plate of said halfarcuate retainer segment includes a pair of longitudinally extendingconvergent flat portions configured and adapted to engage said apertureformed in each of said outer lid portions.
 8. The linear motion bearingassembly of claim 7, further comprising biasing means disposed betweeneach convergent flat portion of said bearing plate and said innersurface of said extended housing retainer structure, said biasing meansextending through said aperture in each of said outer lid portions,wherein each biasing means applies a pre-load to the plurality ofbearing balls disposed in said pair of ball tracks.
 9. The linear motionbearing assembly of claim 8, wherein said pre-load is applied againstopposite sides of said spline at an angle in a range between about 25°to about 75°.
 10. The linear motion bearing assembly of claim 1, whereinsaid plurality of self-contained ball retainer segments areinterengageable.
 11. The linear motion bearing assembly of claim 1,wherein said ball retainer structure is formed of a pair of half arcuateinterengageable self contained ball retainer segments.
 12. The linearmotion bearing assembly of claim 11, wherein each half arcuate retainersegment includes a pair of ball tracks formed therein.
 13. The linearmotion bearing assembly of claim 12, wherein said load bearing portionof each of said pair of ball tracks in said half arcuate retainersegment are arranged in side-by-side configuration within said halfarcuate retainer segment and are separated from one another by adividing member formed in said inner portion of said half arcuateretainer segment.
 14. The linear motion bearing assembly of claim 13,wherein said rail includes a pair of substantially horizontal portionsand an interconnecting web portion thereby defining an interface betweensaid horizontal and said web portions, and wherein said inner portion ofsaid half arcuate retainer segment is configured and adapted to matewith a lateral half of said rail.
 15. The linear motion bearing assemblyof claim 14, wherein said load bearing plates simultaneously engagessaid load bearing portion of each of said pair of ball tracks.
 16. Thelinear motion bearing assembly of claim 15, wherein each of said loadbearing plates includes a central body portion, a pair of longitudinallyextending divergent flat portions, an outer surface, an inner surfaceoriented to be fit into said load bearing plate aperture, and a pair oflongitudinally extending tracks formed along said inner surface, whichpair of tracks serve as an upper surface of said load bearing portionsof said ball bearing tracks.
 17. The linear motion bearing assembly ofclaim 16, further comprising biasing means disposed between said outersurface of each of said load bearing plates and said inner surface ofsaid extended housing retainer structure, wherein said biasing meansincludes an elongate body portion and a pair of elongate divergingcorrugated leaf portions configured and adapted to engage said outersurface of said pair of divergent flat portions of each of said bearingplates, said biasing means applying a pre-load to the plurality ofbearing balls in said load bearing portion of said pair of ball tracks.18. The linear motion bearing assembly of claim 17, wherein saidpre-load is applied to said bearing balls along said interface betweensaid horizontal portion and said web portion of said splined shaft at anangle in a range between about 25° to about 75°.
 19. The linear motionbearing assembly of claim 17, wherein said housing retainer structureincludes a pair of V-shaped projections extending inwardly from an innersurface of said housing structure, and wherein each protrusion engagesan outer surface of said biasing means which in turn presses into saidload bearing plates thereby transmitting said pre-load to said bearingballs and against said interface in said rail.
 20. A linear motionbearing assembly for movement along a rail, the rail including an upperand a lower portion interconnected by a web portion with the upper andlower portions having a width greater than the web portion, the linearmotion bearing assembly, comprising: a ball retainer structure formed ofa pair of half arcuate self-contained ball retainer segments, each ofsaid pair of half arcuate ball retainer segments includes an innerportion defining a pair of ball bearing tracks and having an innersurface configured and adapted to mate with a lateral surface of saidrail, with each ball bearing track having an open load bearing portion,an open return portion, and turnarounds interconnecting said loadbearing and return portions, wherein each load bearing portion of eachball bearing track is disposed adjacent to one another; an outer lidportion defining a load bearing plate aperture formed therein; a loadbearing plate having a central body portion, a pair of longitudinallyextending divergent flat portions, an outer surface, an inner surfaceoriented to be fit into said load bearing plate aperture, and a pair oflongitudinally extending tracks formed along said inner surface, whichpair of tracks serve as an upper surface of said load bearing portionsof said ball bearing tracks; a plurality of bearing balls disposed ineach of said pair of ball bearing tracks for transmitting a load fromsaid rail to said load bearing plate and for facilitating a movement ofsaid linear motion bearing assembly along said rail; an extendinghousing retainer structure including a pair of V-shaped projectionsextending inwardly from an inner surface of said housing structure; andbiasing means having an elongated body portion and a pair of elongatecorrugated leaf portions, said biasing means being disposed between saidouter surface of each of said load bearing plates and said V-shapedprojections of said housing retainer structure, wherein V-shapedprojections press into said biasing means thereby applying a pre-load tosaid plurality of bearing balls in said load bearing portion of saidpair of ball tracks which in turn press into said rail at each juncturebetween said upper and lower portions and said web portion.